• What Is A Nuchal Scan?
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|Terminology: Also known as nuchal translucency scan, first trimester screening, ultra-screen, nuchal fold scan and nuchal translucency ultrasound.
This scan is better known as the 12 week scan (although it can be carried out anywhere between weeks 11 and 13). It is a special ultrasound scan which is performed to specifically measure a tiny bit of fluid that lies under the baby's skin behind the neck known as the nuchal translucency (NT). A maternal blood sample will also be taken and you may also be offered an evaluation of the baby's nasal bone. Together, the results from this combined screening will indicate the risk of a fetal abnormality like Down syndrome being present.
A sonographer (the technician who performs the ultrasound) needs additional training and qualifications to perform this specialized scan. The nuchal scan is a relatively new development but is now routinely carried out in most countries. It is performed in addition to the early trimester scan and the 20 week anatomy scan.
In your early trimester scan your baby is more likely to look like a seahorse than a baby. By week 12 he has grown into a recognizable humanbeing about 8cm long with legs, arms, hands, fingers, a skull, brain and organs. Parents are always surprised by the change in so little time and how active the fetus is during the scan (your baby will be moving about and flexing its developing muscles).
The general cut off measurement for a normal versus suspicious NT measurement is 3mm. Anything over 3mm gives cause for concern and further testing may be advised. This is because fetuses with a measurement over 3mm are at increased risk for chromosome abnormalities like Trisomy 13/Down syndrome. It is not understood why the NT is thicker in such cases, but it has been found that the critical time to take the measurement is between 10.5 and 13 weeks. After 13 weeks the NT can revert to normal, even if the fetus is abnormal. Yet, because the test does not rely just on scan results alone, even after a normal ultrasound you may still get a call a few days later to say the fetus is high risk - this concern will be based on the results from the maternal blood test which checks for specific markers and sometimes the measurement of the fetus nasal bone (if you opted for this additional measurement).
Try not to worry (although we know that's difficult). In the majority of cases, even if the NT result is over 3mm, the fetus is still very likely to be healthy with no chromosome or physical abnormalities. Although the test can detect up to 90 percent of Down syndrome babies, it does not mean if you screen positive that your baby is 90 percent likely to have Down's (this is why the results can be confusing). Based on some complex calculations (which take into account the mother's age, as well as the NT measurement, the presence of blood test markers and fetal nose measurement) you will be told what your ratio risk is. For example you may be told the risk is 1 in 30 or 1 in 4,000 (the first is obviously a much higher risk). If you get a positive result it is just a sign that invasive testing like an amniocentesis test should be offered and additional scanning is necessary as the pregnancy progresses. If you decide not to have invasive testing (which carrys a small risk of miscarriage), you can get more information about your baby's health at the 20 week anatomy scan. This ultrasound can detect problems such as spina bifida, cleft palate, limb abnormalities like clubfoot and congenital heart problems.
The sonographer starts by confirming your baby's gestational age by measuring him from crown to rump. This is to ensure he is about the size he should be for his age. Passing a transducer over your tummy she then focuses in on the baby's neck area - images will show up on a monitor. She measures the thickness of the NT on the screen with calipers. In addition the baby's heart rate will be documented and basic physical structures such as the brain, limbs, stomach and bladder. The scan will also check that amniotic fluid levels, the placenta and the uterus all look normal. The presence and measurement of the baby's nasal bone might also be done at this point if you have opted for it (there is evidence that a short nasal bone can be a sign of fetal abnormality).
Not usually. Although it is possible to guess the gender at the 12 week scan, it is a gamble (you shouldn't choose the nursery color scheme based on it!). Both boys and girls have external genitals at this stage so it’s very easy to make an incorrect prediction. See: How accurate are scans at predicting gender?
Yes. At 12 weeks the baby's anatomy is not fully developed so it can't be accurately evaluated. There are changes in the brain, heart, face, limbs and body which have yet to take place and cannot be fully predicted at this point. The 20 week anatomy scan is a very detailed and extensive examination which is needed to ensure that your baby is developing properly. Also, 12 weeks is too early to learn if the placenta is in a safe area for a vaginal birth and if amniotic fluid levels are within healthy levels.
The average cost, including blood works is between $180 and $280. In most cases (unless a genetic counselor says you are high risk) the fee is not covered by health insurance.
I had a nuchal for my first baby and am not sure if I'd get it again. The test came back indicating the baby was really high risk for Down syndrome. In fact my doctor recommended an abortion. Fortunately I didn't take his advice. My baby ended up being perfect and gorgeous, but I was so stressed I didn't enjoy the pregnancy. It was terrible.
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